Many electronic circuits have a need for a regulated voltage. Conventionally, a regulated voltage is provided as illustrated in FIG. 1. FIG. 1 shows a simple circuit 100 for regulating a voltage (Vout) by using voltage feedback in a loop having a differential amplifier 110. The output of the differential amplifier 110 is coupled to the gate of an output transistor 120. The voltage Vout is taken from the drain of the output transistor 120. A reference voltage (Vref) is input to the negative input of the differential amplifier 110. The voltage at node A is fed into the positive input of the differential amplifier 110. The voltage at node A is some fraction of the voltage Vout, based on the relative sizes of the voltage divider resistors 125 and 130. The circuit 100 keeps the voltage Vout regulated by forcing the voltage at node A to be equal to the reference voltage Vref. By appropriate sizing of voltage divider resistors 125 and 130, a suitable voltage Vout may be maintained.
However, if the voltage reference Vref has a non-zero temperature coefficient, then the voltage Vout will be temperature dependent. Thus, a zero temperature coefficient reference voltage Vref must be supplied to the negative input of the differential amplifier 110. As the circuit 100 regulates the voltage at node A to be equal to the reference voltage Vref, and as the voltage Vout is somewhat larger than this because of the voltage divider resistors 125 and 130, the voltage Vout will exhibit an even larger voltage swing than Vref exhibits as temperature changes.
A second drawback with the conventional circuit 100 of FIG. 1 is the requirement of a differential amplifier 110 and the associated large device count needed to implement the differential amplifier. As chip real estate is a precious commodity, the large device count is undesirable.
Thus, a need exists for a voltage regulation circuit. A further need exists for a voltage regulation circuit that does not require a zero temperature coefficient reference voltage. A still further need exists for a voltage regulation circuit that does not require a differential amplifier to regulate the voltage. A still further need exists for a voltage regulation circuit that is compatible with and can be fabricated economically with existing semiconductor fabrication techniques.